Add Darwin blacklist to GCC torture suite's CMakeLists.txt

Some of these tests use features which are not supported on Darwin. (E.g.
aliases)

As a result of this, there are some unhappy Darwin test suite bots. So, let's
just blacklist those tests when we're targeting Darwin.

Example of unhappy bot:
http://green.lab.llvm.org/green/job/test-suite-verify-machineinstrs-x86_64-O0-g/
diff --git a/SingleSource/Regression/C/gcc-c-torture/execute/CMakeLists.txt b/SingleSource/Regression/C/gcc-c-torture/execute/CMakeLists.txt
index ce8a7b5..a25850f 100644
--- a/SingleSource/Regression/C/gcc-c-torture/execute/CMakeLists.txt
+++ b/SingleSource/Regression/C/gcc-c-torture/execute/CMakeLists.txt
@@ -281,6 +281,22 @@
   list(APPEND TestsToSkip ${SystemZTestsToSkip})
 endif()
 
+# Darwin Test Blacklist
+if(TARGET_OS STREQUAL "Darwin")
+  file(GLOB DarwinTestsToSkip CONFIGURE_DEPENDS
+    # error: aliases are not supported on darwin
+    alias-2.c
+    alias-3.c
+    alias-4.c
+    # Undefined symbols for architecture x86_64:
+    # "_printf_float", referenced from:
+    # -u command line option
+    930513-1.c
+    920501-8.c
+  )
+  list(APPEND TestsToSkip ${DarwinTestsToSkip})
+endif()
+
 ##
 ## Test target setup
 ##